UV monomers and common polymerization inhibitors
Light-curing product is a special product with very high polymerization activity. Its main components – oligomer and active diluent are high polymerization activity of acrylates, another important component – photoinitiator and extremely easy to produce free radicals or cations. In such a mixed system, extremely vulnerable to external light, heat and other effects of polymerization, must be added to the appropriate amount of polymerization inhibitors.
Polymerization inhibitor (polymerization inhibitor) as the name implies is to prevent the occurrence of polymerization of additives. Polymerization inhibitor can terminate all free radicals, so that the polymerization reaction completely stopped. Commonly used inhibitors are phenols, quinones, aromatic amines, aromatic nitro compounds, etc.. Oxygen in the air is a good inhibitor of polymerization, because oxygen itself is a double radical, very easy to combine with free radicals, generate peroxide radicals, initiation activity is greatly reduced, and finally generate monomer and peroxide bonding alternating oligomers. Light-curing products polymerization inhibitors are mainly used phenols, such as p-hydroxyanisole, hydroquinone and 2,6-di-tert-butyl-p-cresol. Due to the addition of hydroquinone, which sometimes causes the system color darkening, is often not used.
In the presence of phenolic polymerization inhibitors, so that the peroxide radical quickly terminated to ensure that the system has a sufficient concentration of oxygen, prolonging the blocking time. Therefore, light-curing products in addition to the addition of phenolic polymerization inhibitors to improve storage stability, but also must pay attention to the storage of the product in the container can not be too full to ensure that there is sufficient oxygen.